Calcium and strontium beta-alumina-phosphors activated by terbium and europium



March 24, 1970 R. AMSTER 3,502,592

CALCIUM AND STRONTIUM (Es-ALUMINA PHOSPHORS ACTIVATED BY TERBIUM AND EUROPIUM Filed July 26, 1967 8 INTENSITY 6 (relative uniis) 4 B 2 n O 1* 200 300 400 500 600 WAVELENGTH (nanometers) CaO-6Al O :0.2OEu :O.25Tb 541 INTENSITY (relative units) 0 WAVELENGTH (nanometers) (Fly. 2.

INVENTO/P.

ROBERT L AMSTER United States Patent 3,502,592 CALCIUM AND STRONTIUM B-ALUMINA- PHOSPHORS ACTIVATED BY TERBIUM AND EUROPIUM Robert L. Amster, Great Neck, N.Y., assignor to General Telephone & Electronics Laboratories Incorporated, a corporation of Delaware Filed July 26, 1967, Ser. No. 656,159 Int. Cl. C09k 1/68 U.S. Cl. 252301.4 6 Claims ABSTRACT OF THE DISCLOSURE A phosphor system consisting of calcium or strontium s-alumina activated by divalent europium and trivalent terbium and having the general formula where Z is an alkaline earth selected from the group consisting of calcium and strontium, x is a quantity in the range 0.025 to 0.25 and y' is a quantity in the range 0.025 to 0.30. These phosphors are photoluminescent and are suitable for use in fluorescent lamps.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to fluorescent materials which emit light in the green region of the spectrum when excited by ultraviolet radiation. In particular, it is related to a series of phosphors comprising calcium or strontium (i-alumina activated by divalent europium and trivalent terbium and to a method for making such phosphors.

Description of the prior art Manganese activated alkaline earth B-alumina phosphors are well known as are luminescent compositions consisting of terbium activated aluminum oxide (see Some Aspects of the Luminescence of Solids, Kroeger, Elsevier Publishing Company, Inc., 1948) Also, as disclosed in my copending U.S. patent application Ser. No. 654,454, filed July 19, 1967, strong green emission may be obtained from calcium fluoride activated by divalent europium and trivalent terbium. Further, it has 'been found that calcium and strontium fl-aluminas activated by terbium exhibit weak green emission which reaches a maximum at approximately 541 nanometers when the material is excited by radiation at about 250 nanometers. Divalent europium alone in these host materials emits fluorescence at 435 nanometers.

SUMMARY OF THE INVENTION I have discovered that when divalent europium is added to trivalent terbium activated calcium or strontium B-alumina the fluorescence intensity of the terbium is greatly enhanced for excitation over the entire 200 to 400 nanometer spectral range. This new phosphor system may be represented by the general formula where Z is an alkaline earth selected from the group consisting of calcium and strontium, x is a quantity in the range 0.025 to 0.25 and y is a quantity in the range 0.025 to 0.30.

Divalent europium has a broad absorption band in the ultraviolet region extending from 200 to 400 nanometers and much of the energy absorbed by the divalent europium is transferred to the trivalent terbium ions which then emit their characteristic fluorescence. Thus,

3,502,592 Patented Mar. 24, 1970 trivalent terbium emission is sensitized by divalent europlum. The strong emission in the band centered at 435 nanometers in The phosphor may be synthesized by dry blending europium oxide, Eu O and terbium oxide, Tb O with powdered alumina A1 0 and a fluoride composition defined by the formula ZF wherein Z is selected from the group'consisting of calcium and strontium. The mixture is fired for three hours at approximately 1150 C. in an hydrogen atmosphere, removed from the furnace and allowed to cool to room temperature. This method provides a more rapid and complete reaction than known methods of producing CaO-6Al O and SrO-6Al O wherein oxy compounds of calcium and strontium are fired in air.

BRIEF DESCRIPTION OF THE DRAWING FIG 1 illustrates the excitation and emission curves for CaO-6Al O :Tb and FIG. 2 shows, to the same scale as FIG. 1, the excitation and emission curves for one of the phosphors of the present invention CaO-6Al O :Eu +,Tb

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I 0.07 gram of powdered Eu O and 0.09 gram of Tb O were dry blended with 1.2 grams of powdered A1 0 and 0.18 gram of CaF The blend was placed in an alumina boat and fired in a quartz reaction tube located in a tube furnace. The temperature in the furnace was brought from ambient to 1150 C., and held at that temperature for three hours. The reaction tube was then removed from the furnace and allowed to cool to room temperature.

The resultant phosphor was excited by radiation in the range 200 to 400 nanometers. Excitation curve A of FIG. 2 was obtained by measuring the intensity of the radiation fromthe phosphor at 541 nanometers as the excitation wavelength was varied through the 200 to 400 nanometer range. As shown,

7 emission was obtained over a wide range of excitation shown at B in FIG. 1 indicates that the peak emission for both materials is obtained at 541 nanometers. However, the peak intensity of CaO-6Al O :0.25Tb is less than one fiftieth than obtained from the phosphor Emission curve B of FIG. 1 was obtained by exciting CaO-6Al O :0.25Tb-'+ with radiation having a wavelength of Y250 nanometers, the value producing maximum fluorescence at 541 nanometers.

3 relativeintensity of CaO-6Al O :0.20Eu 0.25Tb

was also obtained by comparing it With the emission from a commercially available green-emitting phosphor, manganese activated Zinc silicate, under medium and low pressure mercury lamp excitation. The results were as follows:

Relative intensities 7 Medium pressure Low pressure F'hosphor Hg lamp Hg lamp zu2si04=Mn (standar W 100* 100 3aO-6AlzO =0.20Eu 0.25Tb 670 65 Example 11 A phosphor was prepared by the method of Example I except that 0.3 gram of SrF were blended with 0.07 gram of Eu O 0.09 gram of Tb O and 1.2 grams of powdered A1 The resultant phosphor Example IV Additional samples were prepared of phosphor compo- ;itions having the formula? SrO-6Al O :xEu yTb in which x and y were varied between the same limits as in Example III. Again, green emitting phosphors were obtained but their intensities were somewhat less than that. exhibited by the phosphors of Examples I and all.

What is claimed is:

l. A phosphor composition defined by the formul ZO-6Al O :xEu yTb wherein Z an alkaline earth selected from thegroup eonsisting' of calcium and strontium, x is a quantity in the range 0.025 to 0.25 and y is a quantity in therange 0.025 to 0.30.

2. The composition of matter defined by claim 1 where Z is calcium. 7

3. The composition of matter defined by claim 1 where Z is strontium. i

4. The composition of matter defined by claim 2 where x equals approximately 0.20 and y equals approximately 0.25. 1

5. The composition of matter defined by claim 3 where x equais approximately .020 and y equals: approximately 0.25. r

6. The method of preparing a phosphor having the formula ZO-6Al O :Eu Tb ,where Z is selected from the group consisting of zealcium and strontium, comprising I the steps of 'a (a) blending europium oxide and terbium oxide with alumina and :a fluoride composition defined by the formula ZF the molar ratio of ZF to alumina being between 1 and 6;, I

(b) firing the blend for approximately three hours at 1150 C. in a hydrogen atmosphere, and

(c) allowing the resultant phosphor to cool to room temperature.

'Referen'ees Cited UNITED STATES PATENTS 12/1e66 Lange 252-1014 12/1963 Brixner 25262.63 

